In every contract, CAI seeks a $25\%$ advance payment which is non$-$refundable in case the buyer cancels the contract soon after signature. While negotiating with the buyer, CAI had to remove the "non$-$refundable" clause. Which of the following could CAI request from the buyer to help warrant the advance payment it will need to pay?

A$)$ Letter of guarantee

B$)$ Documentary letter of credit at sight

C$)$ Red clause letter of credit

D$)$ Confirmed letter of guarantee